dyndbg: pr_fmt(fmt) with additional arguments?

dyndbg: pr_fmt(fmt) with additional arguments?

[Philipp Hahn]

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Hello Jason, hello Jim,

I've been using the following in my modules to prefix all messages with
the module and function name:
	#define pr_fmt(fmt) KBUILD_MODNAME ".%s ", __func__

This worked nicely until `pr_debug_ratelimit()` is used: The additional
arguments breaks `DEFINE_DYNAMIC_DEBUG_METADATA_CLS`:

	#define pr_debug_ratelimited(fmt, ...)					\
		DEFINE_DYNAMIC_DEBUG_METADATA(…, pr_fmt(fmt));		\

	#define DEFINE_DYNAMIC_DEBUG_METADATA(name, fmt)		\
		DEFINE_DYNAMIC_DEBUG_METADATA_CLS(name, …, fmt)

	#define DEFINE_DYNAMIC_DEBUG_METADATA_CLS(name, cls, fmt)	\
		static struct _ddebug  __aligned(8)			\
		__section("__dyndbg") name = {				\
			… \
			.format = (fmt),				\

This could be fixed easily by adding an additional '...' to it to slurp
any additional argument which `pr_fmt` might add.

Would this be okay or do I miss something?

For testing I have recompiled current 7.0.0-rc1 for x86_64 with no
compile failures.

Philipp Hahn

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From 545173a75e3928ec000b1127bfc99439b7fa2f8b Mon Sep 17 00:00:00 2001
Message-ID: <545173a75e3928ec000b1127bfc99439b7fa2f8b.1772186702.git.p.hahn@avm.de>
From: Philipp Hahn <phahn-oss@avm.de>
Date: Fri, 27 Feb 2026 10:53:04 +0100
Subject: [PATCH] dyndbg: Ignore additional arguments from pr_fmt
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Organization: FRITZ! Technology GmbH, Berlin, Germany

pr_fmt can be used to add a common prefix to any output from a module:
	#define pr_fmt(fmt) KBUILD_MODNAME ".%s ", __func__

But adding additional arguments breaks dynamic debug:
> error: macro "DEFINE_DYNAMIC_DEBUG_METADATA_CLS" passed 4 arguments, but takes just 3
> |         pr_debug_ratelimited("%s", "Hello world!");
> |                                                  ^
> note: macro "DEFINE_DYNAMIC_DEBUG_METADATA_CLS" defined here
> | #define DEFINE_DYNAMIC_DEBUG_METADATA_CLS(name, cls, fmt)       \
> |
> error: ‘DEFINE_DYNAMIC_DEBUG_METADATA_CLS’ undeclared (first use in this function)
> |         DEFINE_DYNAMIC_DEBUG_METADATA_CLS(name, _DPRINTK_CLASS_DFLT, fmt)
> |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> note: in expansion of macro ‘DEFINE_DYNAMIC_DEBUG_METADATA’
> |         DEFINE_DYNAMIC_DEBUG_METADATA(descriptor, pr_fmt(fmt));         \
> |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> note: in expansion of macro ‘pr_debug_ratelimited’
> |         pr_debug_ratelimited("%s", "Hello world!");
> |         ^~~~~~~~~~~~~~~~~~~~

Add an additional ', ...' to DEFINE_DYNAMIC_DEBUG_METADATA_CLS to slurp
any additional argument, which `pr_fmt` might add.

Signed-off-by: Philipp Hahn <phahn-oss@avm.de>
---
 include/linux/dynamic_debug.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index 05743900a1169..0ac0df04bac00 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -167,7 +167,7 @@ void __dynamic_ibdev_dbg(struct _ddebug *descriptor,
 		dump_stack();					\
 }
 
-#define DEFINE_DYNAMIC_DEBUG_METADATA_CLS(name, cls, fmt)	\
+#define DEFINE_DYNAMIC_DEBUG_METADATA_CLS(name, cls, fmt, ...)	\
 	static struct _ddebug  __aligned(8)			\
 	__section("__dyndbg") name = {				\
 		.modname = KBUILD_MODNAME,			\
-- 
2.43.0

Re: dyndbg: pr_fmt(fmt) with additional arguments?

[Philipp Hahn]

Hello,

Am Fri, Feb 27, 2026 at 12:33:18PM +0100 schrieb Philipp Hahn:
> I've been using the following in my modules to prefix all messages with
> the module and function name:
> 	#define pr_fmt(fmt) KBUILD_MODNAME ".%s ", __func__

<https://docs.kernel.org/core-api/printk-basics.html> itself has the
following example:

> #define pr_fmt(fmt) "%s:%s: " fmt, KBUILD_MODNAME, __func__

This breaks pr_debug_ratelimited().

> This could be fixed easily by adding an additional '...' to
> `DEFINE_DYNAMIC_DEBUG_METADATA_CLS(name, cls, fmt)` to slurp any
> additional argument which `pr_fmt` might add.
> 
> Would this be okay or do I miss something?
> 
> For testing I have recompiled current 7.0.0-rc1 for x86_64 with no
> compile failures.

Ping?

Philipp Hahn

> From 545173a75e3928ec000b1127bfc99439b7fa2f8b Mon Sep 17 00:00:00 2001
> Message-ID: <545173a75e3928ec000b1127bfc99439b7fa2f8b.1772186702.git.p.hahn@avm.de>
> From: Philipp Hahn <phahn-oss@avm.de>
> Date: Fri, 27 Feb 2026 10:53:04 +0100
> Subject: [PATCH] dyndbg: Ignore additional arguments from pr_fmt
> MIME-Version: 1.0
> Content-Type: text/plain; charset=UTF-8
> Content-Transfer-Encoding: 8bit
> Organization: FRITZ! Technology GmbH, Berlin, Germany
> 
> pr_fmt can be used to add a common prefix to any output from a module:
> 	#define pr_fmt(fmt) KBUILD_MODNAME ".%s ", __func__
> 
> But adding additional arguments breaks dynamic debug:
> > error: macro "DEFINE_DYNAMIC_DEBUG_METADATA_CLS" passed 4 arguments, but takes just 3
> > |         pr_debug_ratelimited("%s", "Hello world!");
> > |                                                  ^
> > note: macro "DEFINE_DYNAMIC_DEBUG_METADATA_CLS" defined here
> > | #define DEFINE_DYNAMIC_DEBUG_METADATA_CLS(name, cls, fmt)       \
> > |
> > error: ‘DEFINE_DYNAMIC_DEBUG_METADATA_CLS’ undeclared (first use in this function)
> > |         DEFINE_DYNAMIC_DEBUG_METADATA_CLS(name, _DPRINTK_CLASS_DFLT, fmt)
> > |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > note: in expansion of macro ‘DEFINE_DYNAMIC_DEBUG_METADATA’
> > |         DEFINE_DYNAMIC_DEBUG_METADATA(descriptor, pr_fmt(fmt));         \
> > |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > note: in expansion of macro ‘pr_debug_ratelimited’
> > |         pr_debug_ratelimited("%s", "Hello world!");
> > |         ^~~~~~~~~~~~~~~~~~~~
> 
> Add an additional ', ...' to DEFINE_DYNAMIC_DEBUG_METADATA_CLS to slurp
> any additional argument, which `pr_fmt` might add.
> 
> Signed-off-by: Philipp Hahn <phahn-oss@avm.de>
> ---
>  include/linux/dynamic_debug.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
> index 05743900a1169..0ac0df04bac00 100644
> --- a/include/linux/dynamic_debug.h
> +++ b/include/linux/dynamic_debug.h
> @@ -167,7 +167,7 @@ void __dynamic_ibdev_dbg(struct _ddebug *descriptor,
>  		dump_stack();					\
>  }
>  
> -#define DEFINE_DYNAMIC_DEBUG_METADATA_CLS(name, cls, fmt)	\
> +#define DEFINE_DYNAMIC_DEBUG_METADATA_CLS(name, cls, fmt, ...)	\
>  	static struct _ddebug  __aligned(8)			\
>  	__section("__dyndbg") name = {				\
>  		.modname = KBUILD_MODNAME,			\
> -- 
> 2.43.0
> 

Re: dyndbg: pr_fmt(fmt) with additional arguments?

[jim.cromie]

On Fri, Feb 27, 2026 at 4:12 AM Philipp Hahn <phahn-oss@avm.de> wrote:
>
> Hello Jason, hello Jim,
>
> I've been using the following in my modules to prefix all messages with
> the module and function name:
>         #define pr_fmt(fmt) KBUILD_MODNAME ".%s ", __func__

Your example loses the fmt, so is not actually useful.

but that said, the compile err is real, I hit it once I changed

1 - the pr_debug("exited") call in test_dynamic_debug.c
     to pr_debug_ratelimited.

2- the pr_fmt in same:
 #if defined(TEST_DYNAMIC_DEBUG_SUBMOD)
-  #define pr_fmt(fmt) "test_dd_submod: " fmt
+  #define pr_fmt(fmt) KBUILD_MODNAME " test_dd_submod: %s" fmt, __func__

2 was my test-case, on my latest branch, yours (on master) will be different.

please add that test to your patch, and my
Acked-by: Jim Cromie <jim.cromie@gmail.com>

>
> This worked nicely until `pr_debug_ratelimit()` is used: The additional
> arguments breaks `DEFINE_DYNAMIC_DEBUG_METADATA_CLS`:
>
>         #define pr_debug_ratelimited(fmt, ...)                                  \
>                 DEFINE_DYNAMIC_DEBUG_METADATA(…, pr_fmt(fmt));          \
>
>         #define DEFINE_DYNAMIC_DEBUG_METADATA(name, fmt)                \
>                 DEFINE_DYNAMIC_DEBUG_METADATA_CLS(name, …, fmt)
>
>         #define DEFINE_DYNAMIC_DEBUG_METADATA_CLS(name, cls, fmt)       \
>                 static struct _ddebug  __aligned(8)                     \
>                 __section("__dyndbg") name = {                          \
>                         … \
>                         .format = (fmt),                                \
>
> This could be fixed easily by adding an additional '...' to it to slurp
> any additional argument which `pr_fmt` might add.
>
> Would this be okay or do I miss something?
>
> For testing I have recompiled current 7.0.0-rc1 for x86_64 with no
> compile failures.
>
> Philipp Hahn

I tried this locally, it built and ran w/o errors.

Ackd-by: Jim Cromie <jim.cromie@gmail.com>

[PATCH v2] dyndbg: Ignore additional arguments from pr_fmt

[Philipp Hahn]

pr_fmt can be used to add a common prefix to any output from a module:
	#define pr_fmt(fmt) KBUILD_MODNAME ".%s " fmt, __func__

But adding additional arguments breaks dynamic debug:
> error: macro "DEFINE_DYNAMIC_DEBUG_METADATA_CLS" passed 4 arguments, but takes just 3
> |         pr_debug_ratelimited("%s", "Hello world!");
> |                                                  ^
> note: macro "DEFINE_DYNAMIC_DEBUG_METADATA_CLS" defined here
> | #define DEFINE_DYNAMIC_DEBUG_METADATA_CLS(name, cls, fmt)       \
> |
> error: ‘DEFINE_DYNAMIC_DEBUG_METADATA_CLS’ undeclared (first use in this function)
> |         DEFINE_DYNAMIC_DEBUG_METADATA_CLS(name, _DPRINTK_CLASS_DFLT, fmt)
> |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> note: in expansion of macro ‘DEFINE_DYNAMIC_DEBUG_METADATA’
> |         DEFINE_DYNAMIC_DEBUG_METADATA(descriptor, pr_fmt(fmt));         \
> |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> note: in expansion of macro ‘pr_debug_ratelimited’
> |         pr_debug_ratelimited("%s", "Hello world!");
> |         ^~~~~~~~~~~~~~~~~~~~

Add an additional ', ...' to DEFINE_DYNAMIC_DEBUG_METADATA_CLS to slurp
any additional argument, which `pr_fmt` might add.

Signed-off-by: Philipp Hahn <phahn-oss@avm.de>
Acked-by: Jim Cromie <jim.cromie@gmail.com>
---
 include/linux/dynamic_debug.h | 2 +-
 lib/test_dynamic_debug.c      | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index 05743900a1169..0ac0df04bac00 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -167,7 +167,7 @@ void __dynamic_ibdev_dbg(struct _ddebug *descriptor,
 		dump_stack();					\
 }
 
-#define DEFINE_DYNAMIC_DEBUG_METADATA_CLS(name, cls, fmt)	\
+#define DEFINE_DYNAMIC_DEBUG_METADATA_CLS(name, cls, fmt, ...)	\
 	static struct _ddebug  __aligned(8)			\
 	__section("__dyndbg") name = {				\
 		.modname = KBUILD_MODNAME,			\
diff --git a/lib/test_dynamic_debug.c b/lib/test_dynamic_debug.c
index 77c2a669b6afd..cf1e3b5f6f0f8 100644
--- a/lib/test_dynamic_debug.c
+++ b/lib/test_dynamic_debug.c
@@ -6,7 +6,7 @@
  *      Jim Cromie	<jim.cromie@gmail.com>
  */
 
-#define pr_fmt(fmt) "test_dd: " fmt
+#define pr_fmt(fmt) "test_dd: %s " fmt, __func__
 
 #include <linux/module.h>
 
@@ -155,7 +155,7 @@ static int __init test_dynamic_debug_init(void)
 
 static void __exit test_dynamic_debug_exit(void)
 {
-	pr_debug("exited\n");
+	pr_debug_ratelimited("exited\n");
 }
 
 module_init(test_dynamic_debug_init);
-- 
2.43.0

Re: dyndbg: pr_fmt(fmt) with additional arguments?

[Philipp Hahn]

Hello Jim,

Am Sun, Mar 15, 2026 at 05:30:43PM -0600 schrieb jim.cromie@gmail.com:
> On Fri, Feb 27, 2026 at 4:12 AM Philipp Hahn <phahn-oss@avm.de> wrote:
> >
> > Hello Jason, hello Jim,
> >
> > I've been using the following in my modules to prefix all messages with
> > the module and function name:
> >         #define pr_fmt(fmt) KBUILD_MODNAME ".%s ", __func__
> 
> Your example loses the fmt, so is not actually useful.

Yes, somehow that 'fmt' got lost; I've re-added it.

> but that said, the compile err is real, I hit it once I changed
> 
> 1 - the pr_debug("exited") call in test_dynamic_debug.c
>      to pr_debug_ratelimited.
> 
> 2- the pr_fmt in same:
>  #if defined(TEST_DYNAMIC_DEBUG_SUBMOD)
> -  #define pr_fmt(fmt) "test_dd_submod: " fmt
> +  #define pr_fmt(fmt) KBUILD_MODNAME " test_dd_submod: %s" fmt, __func__
> 
> 2 was my test-case, on my latest branch, yours (on master) will be different.
> 
> please add that test to your patch, and my
> Acked-by: Jim Cromie <jim.cromie@gmail.com>

I did both; v2 is on it's way. Thank you for your review.

Philipp Hahn